Page 61 - Probability Demystified

50 CHAPTER 3 The Addition Rules

PRACTICE

1. When a card is selected at random from a 52-card deck, find the
probability that the card is a face card or a spade.
2. A die is rolled. Find the probability that the result is an even number
or a number less than 3.
3. Two dice are rolled. Find the probability that a number on one die is
a six or the sum of the spots is eight.
4. A coin is tossed and a die is rolled. Find the probability that the coin
falls heads up or that there is a 4 on the die.
5. In a psychology class, there are 15 sophomores and 18 juniors. Six of
the sophomores are males and 10 of the juniors are males. If a student
is selected at random, find the probability that the student is
a. A junior or a male.
b. A sophomore or a female.
c. A junior.

ANSWERS

1. P(face card or spade) ¼ P(face card) þ P(spade) P(face card and
12 13 3 22 11
spade) ¼ þ ¼ ¼
52 52 52 52 26
2. P(even or less than three) ¼ P(even) þ P(less than three) P(even and
3 2 1 4 2
less than three) ¼ þ ¼ ¼
6 6 6 6 3
3. P(6 or a sum of 8) ¼ P(6) þ P(sum of 8) P(6 and sum of 8) ¼
11 5 2 14 7
þ ¼ ¼
36 36 36 36 18
1 1 1 7
4. P(heads or 4) ¼ P(heads) þ P(4) P(heads and 4) ¼ þ ¼
2 6 12 12
5. a. P( junior or male) ¼ P( junior) þ P(male) P( junior and male) ¼
18 16 10 24 8
þ ¼ ¼
33 33 33 33 11
b. P(sophomore or female) ¼ P(sophomore) þ P(female)
15 17 9 23
P(sophomore or female) ¼ þ ¼
33 33 33 33
18 6
c. P( junior) ¼ ¼
33 11